Roller cone bits, methods, and systems with anti-tracking variation in tooth orientation

ABSTRACT

A roller cone drill bit in which the orientations of the teeth are varied within a single row, and/or between the heel row of one cone and the heel row of another cone, to prevent tracking.

CROSS-REFERENCE TO OTHER APPLICATION

This application is a Continuation of U.S. patent application Ser. No.10/162,413, filed Jun. 3, 2002, which is a Continuation of U.S. patentapplication Ser. No. 09/523,474, filed Mar. 10, 2000, now U.S. Pat. No.6,401,839, which is a Continuation-In-Part of U.S. patent applicationSer. No. 09/387,304, filed Aug. 31, 1999, now U.S. Pat. No. 6,095,262,which claims priority from U.S. provisional application 60/098,442 filedAug. 31, 1998 , which is hereby incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates generally to the drilling of oil and gaswells, or similar drilling operations, and in particular to orientationof tooth angles on a roller cone drill bit.

Rotary Drilling

Oil wells and gas wells are drilled by a process of rotary drilling,using a drill rig such as is shown in FIG. 5. In conventional verticaldrilling, a drill bit 50 is mounted on the end of a drill string 52(drill pipe plus drill collars), which may be miles long, while at thesurface a rotary drive (not shown) turns the drill string, including thebit at the bottom of the hole.

Two main types of drill bits are in use, the fixed or drag bit, seen inFIG. 4, and the roller cone bit, seen in FIG. 3. In the roller cone bita set of cones 36 (two are visible in this drawing) having teeth orcutting inserts 38 are arranged on rugged bearings on the arms 37 of thebit. As the drill string is rotated, the cones will roll on the bottomof the hole, and the teeth or cutting inserts will crush the formationbeneath them. Drilling fluid, which is pumped down the drill stringunder pressure, is directed out nozzles 34, to provide cleaning of thebit and to sweep broken fragments of rock uphole.

Roller Cone Bit Design

FIG. 2 is view from the bottom of a roller cone bit which has threecones 201, 202, and 203, each containing rows of chisel-shaped inserts210 for cutting elements. It can be noted that the “cones” in a rollercone bit need not be perfectly conical (nor perfectly frustroconical),but often have a slightly swollen axial profile. Moreover, the axes ofthe cones do not have to intersect the centerline of the borehole, ascan be seen in this drawing. (The angular difference is referred to asthe “offset” angle.) Another variable is the angle by which thecenterline of the bearings intersects the horizontal plane of the bottomof the hole, and this angle is known as the journal angle. Thus as thedrill bit is rotated, the cones typically do not roll true, and acertain amount of gouging and scraping takes place. The gouging andscraping action is complex in nature, and varies in magnitude anddirection depending on a number of variables.

It should also be noted that while each cone has a row of teethcircumscribing its greatest circumference (this is the heel, or gage,row), the other rows of teeth are offset so that no two cones have teethwhich will intersect each other as they rotate.

Conventional roller cone bits can be divided into two broad categories:Insert bits and steel-tooth bits. Steel tooth bits are utilized mostfrequently in softer formation drilling, whereas insert bits areutilized most frequently in medium and hard formation drilling.

Steel-tooth bits have steel teeth formed integral to the cone. (Ahard-facing is typically applied to the surface of the teeth to improvethe wear resistance of the structure.) Insert bits have very hardinserts (e.g. specially selected grades of tungsten carbide)press-fitted into holes drilled into the cone surfaces. The insertsextend outwardly beyond the surface of the cones to form the “teeth”that comprise the cutting structures of the drill bit.

The design of the component elements in a rock bit are interrelated(together with the size limitations imposed by the overall diameter ofthe bit), and some of the design parameters are driven by the intendeduse of the product. For example, cone angle and offset can be modifiedto increase or decrease the amount of bottom hole scraping. Many otherdesign parameters are limited in that an increase in one parameter maynecessarily result in a decrease of another. For example, increases intooth length may cause interference with the adjacent cones.

Tooth Design

The teeth of steel tooth bits are predominantly of the inverted “V”shape. The included angle (i.e. the sharpness of the tip) and the lengthof the tooth will vary with the design of the bit. In bits designed forharder formations the teeth will be shorter and the included angle willbe greater. Gage row teeth (i.e. the teeth in the outermost row of thecone, next to the outer diameter of the borehole) may have a “T” shapedcrest for additional wear resistance.

The most common shapes of inserts are spherical, conical, and chisel.Spherical inserts have a very small protrusion and are used for drillingthe hardest formations. Conical inserts have a greater protrusion and anatural resistance to breakage, and are often used for drilling mediumhard formations.

Chisel shaped inserts have opposing flats and a broad elongated crest,resembling the teeth of a steel tooth bit. Chisel shaped inserts areused for drilling soft to medium formations. The elongated crest of thechisel insert is normally oriented in alignment with the axis of conerotation, as can be seen in FIG. 2. Thus, unlike spherical and conicalinserts, the chisel insert may be directionally oriented about itscenter axis. (This is true of any tooth which is not axially symmetric.)The angle of orientation is measured as a deviation from the planeintersecting the center of the cone and the center of the tooth.

Roller Cone Tracking

The study of bottom hole patterns has allowed engineers to evaluateperformance and to begin to reduce such phenomena as tracking. FIG. 6Ashows a computer generated pattern of the impressions of the teeth of asingle roller cone on the hole bottom after a single revolution of thebit, showing a large separation between the individual teethimpressions, and between the rows on the cone.

FIG. 6C shows the impression of all of the cones on the bit after asingle revolution of the bit. Note that while the inner rows of teethfrom different cones do not generally follow the same path as theytraverse the hole bottom, the teeth in the heel row of all of the conestend to follow a single path on the outer circumference of the hole.

Tracking occurs when the teeth of a drill bit fall into the impressionsin the formation formed by other teeth at a preceding moment in timeduring the revolution of the drill bit. FIG. 6B shows an impression of asingle cone on the hole bottom after two revolutions of the bit. In thiscase, many of the impressions from the first revolution are partiallyoverlain by the impressions of that same row from the second revolution.This overlapping will put lateral pressure on the teeth, tending tocause the cone to align with the previous impressions. Tracking can alsohappen when teeth of one cone's heel row fall into the impressions madeby the teeth of another cone's heel row. Tracking results in slow ratesof penetration, detrimental wear of the cutting structures and prematurefailure of bits.

Bit Design to Prevent Tracking

The economics of drilling a well are strongly reliant on rate ofpenetration, which is itself strongly affected by the design of thecutting structures. Currently, roller cone bit designs remain the resultof generations of modifications made to original designs. Themodifications are based on years of experience in evaluating bitrecords, dull bit conditions, and bottom hole patterns, but these bitdesigns have not solved the issue of tracking.

One method commonly used to discourage bit tracking is known as astaggered tooth design. In this design the teeth are located at unequalintervals along the circumference of the cone. This is intended tointerrupt the recurrent pattern of impressions on the bottom of thehole. However, staggered tooth designs do not prevent tracking of theoutermost rows of teeth, where the teeth are encountering impressions inthe formation left by teeth on other cones. Staggered tooth designs alsohave the short-coming that they can cause fluctuations in conerotational speed and increased bit vibration.

U.S. Pat. No. 5,197,555 to Estes discloses milled-tooth cones with “thegage [row] of one cone oblique to the leading side and the gage row ofanother cone oblique to the trailing side”.

Roller Cone Bits, Methods and Systems with Anti-Tracking Variation inTooth Orientation

The present application discloses new bit and cone designs, as well asmethods of design and systems and drilling methods using these designs,in which variation in tooth orientation is used to reduce tracking. (Ofcourse, tooth orientation is only relevant if the teeth are notaxisymmetric, e.g. with chisel shaped insert teeth.) At least twoclasses of embodiments are disclosed, which can be used separately or(to achieve a synergistic result) together.

The parent application described bit design procedures using control oftooth orientation as one of the design variables. In implementing thoseprocedures, the present inventor realized that the variation in toothorientation which is described in that application can also achieve asubstantial improvement in tracking resistance. When one tooth'sintrusion into the formation partly overlaps the impression made by apreceding tooth, a lateral force will result which tends to align theintrusion with the impression. However, the present inventor hasrealized that, when a tooth's orientation does NOT allow it to fully fitinto the impression made by a previous tooth, the lateral force tendingto pull the tooth toward the impression will be reduced (thoughtypically not eliminated). By varying tooth orientation to avoid perfectfit between an impression and a following tooth (in some cases), thepropensity to track can be reduced. The less perfect the match betweenone tooth and another, the more the propensity to track is reduced; forexample, with chisel-shaped teeth, the maximum reduction in lateralforce is achieved if a tooth is 90 degrees out of alignment with afollowing tooth; but significant reductions can be achieved even with 30degrees of misalignment.

Application Ser. No. 09/387,304 (now U.S. Pat. No. 6,095,262), filedAug. 31, 1999 and which is hereby incorporated by reference, discloses amethod of optimizing the tooth orientation on a cone. It is hereindisclosed that within an optimal range of orientations, the toothorientation within a single row or between the heel rows of two or morecones can be varied to lessen the propensity for tracking. It isunderstood in this context that references to “tooth” or “teeth” includeboth milled teeth and elongated inserts, and that the invention is notspecifically limited to the use of steel teeth.

In one class of embodiments, the orientations of the teeth are variedbetween the heel row of one cone and the heel row of another cone. Sincethe heel rows of all three cones normally follow the same path,reduction in tracking propensity is particularly useful here.

In another class of embodiments, the orientations of the teeth arevaried within a single row of a cone. This helps to avoid same-rowtracking forces: tracking is not only caused by the impressions of apreceding cone. The inner rows of teeth are usually spaced so that notwo rows follow the same path on the cutting face; but a single row ofteeth, on a single cone, will still encounter the impressions left byits own previous path. Since a full circle of a row's path will notnecessarily be an exact multiple of the spacing of impressions on thecutting face, the misalignment of teeth to previous impressions mayindeed contribute a lateral force component. Here too a difference inorientation between tooth and impression helps to reduce this lateralforce component. The different tooth orientations can be grouped inblocks in a given row, such as a block of teeth with orientation A whichextends over half the row circumference and a block of teeth withorientation B which extends over the other half; or blocks ABAB, whereeach block extends over 90 degrees; or blocks ABC; or the blocks canhave unequal numbers of teeth.

The disclosed innovations, in various embodiments, provide one or moreof at least the following advantages:

-   -   reduces propensity to track rows on different cones that drill        the same circumferential path of the hole bottom;    -   reduces propensity to track the other teeth on the same row of a        cone;    -   minimizes vibration during drilling;    -   increases lifetime of drill bit and drill string components;    -   reduces drilling cost-per-foot.

BRIEF DESCRIPTION OF THE DRAWING

The disclosed inventions will be described with reference to theaccompanying drawings, which show important sample embodiments of theinvention and which are incorporated in the specification hereof byreference, wherein:

FIGS. 1A to 1C are schematic side views of first, second, and thirdcones of a drill bit showing only their heel rows, which are oriented inaccordance with a preferred embodiment of the present invention.

FIG. 1D is a schematic side view of a drill bit cone showing only aninner row of teeth oriented in accordance with a preferred embodiment ofthe present invention.

FIG. 2 is a view from the bottom of a conventional drill bit havingthree cones with chisel inserts for teeth.

FIG. 3 is a side view of a conventional roller cone bit.

FIG. 4 is a side view of a conventional drag bit.

FIG. 5 is a side view schematic of a drilling rig.

FIGS. 6A-C are examples respectively of the impression distribution onthe hole bottom of A) a first cone on a drill bit after one bitrevolution, B) a first cone on a drill bit after two bit revolutions,showing how tracking can occur, and C) all teeth of a bit after one bitrevolution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The numerous innovative teachings of the present application will bedescribed with particular reference to the presently preferredembodiment (by way of example, and not of limitation).

Application Ser. No. 09/387,304 (now U.S. Pat. No. 6,095,262), filedAug. 31, 1999, discloses a method of determining the trajectory of eachtooth as it traverses the hole bottom, then using this information tooptimize the orientation of the teeth accordingly. In all examplesdiscussing the orientation of the teeth, it is understood that allangles will be chosen to be within an optimal range, as determined bythis or similar method, so that drilling efficiency is not adverselyaffected.

FIG. 1A is schematic side view of first cone 102 of a three-cone bit inaccordance with a preferred embodiment of the present disclosure. Thisdiagram shows only one tooth in the outermost or gage row, however itwill be understood that the cone has multiple rows of teeth, withmultiple teeth in the rows. The tooth shown in cone 102 in the outermostrow 104 has chisel shaped inserts 106 in which the elongated portion ofchisel inserts 106 are orientated at an angle A, here 160 degrees fromthe center axis of rotation of cone 102

FIG. 1B is schematic side view of a second cone 112 of the same rollercone bit. Cone 112 has an outermost row 114 having chisel shaped inserts116 in which the elongated portion of the chisel inserts are oriented atan angle B, here 140 degrees from the center axis of rotation of cone112. Principle to this embodiment is that angle A and angle B are notthe same, but both are within the optimal range of angles as determinedby the method of application Ser. No. 09/387,304 (now U.S. Pat. No.6,095,262), filed Aug. 31, 1999. In this configuration, teeth 106 offirst cone 102, and teeth 116 of second cone 112 are thus aligned indifferent orientations. The difference in orientation causes thegeneration of dissimilar impressions in the hole bottom pattern by teeth106 and teeth 116. Tracking by the consecutive engagement of teeth 106,and teeth 116 with the formation is thus prevented.

FIG. 1C is a schematic side view of a cone 122 of the same roller conebit. Cone 122 has an outermost row 124 having chisel shaped inserts 126in which the elongated portion of chisel inserts 126 are orientated atan angle C, here 160 degrees from the center axis of rotation of cone122. Note that angle C is different from both angle A and angle B, butwill still be within the optimal range determined for this location.

FIG. 1D is a schematic side view of a cone 132 of a roller cone bit.Cone 132 has an inner row 134 having chisel shaped inserts 136 in whichthe elongated portion of chisel inserts 136 are orientated at an angleD, here 20 degrees from the center axis of rotation of cone 132. Also ininner row 134, are chisel inserts 138, in which the elongated portion ofthe chisel inserts is orientated at an angle E, here 40 degrees from thecenter axis of rotation of cone 132. Principle to this embodiment isthat angle D and angle E are not the same, but are within an optimalrange. In this configuration, teeth 136 of row 134, and teeth 138 of row134 are thus aligned in different orientations. The difference inorientation causes the generation of dissimilar impressions on the holebottom by teeth 136 and teeth 138. Tracking by the consecutiveengagement of teeth 136, and teeth 138 with the formation is thusprevented.

OPERATION OF THE INVENTION

In the operation of the preferred embodiment, a roller cone rock bit hasa first cone 102 having an outermost row 104 of teeth 106 oriented at anangle A degrees to the center axis of cone 102. The roller cone rock bithas a second cone 112 having an outermost row 114 of teeth 116 orientedat an angle B degrees to the center axis of cone 112. Since angle A doesnot equal angle B, teeth 106 of first cone 102, and teeth 116 of secondcone 112 are thus aligned at different orientations. When operatingtorque and weight are applied to the rock bit, teeth 106 and teeth 116will engage the formation of the hole bottom and crush and scrap theformation away. In doing so, each engagement of teeth 106 and teeth 116results in the creation of a crater in the hole bottom. The shape andsize of the craters depends in a large part on the precise orientationsof teeth 106 and teeth 116 in relation to the center axes of respectivefirst cone 102 and second cone 112. The difference in orientation causesthe generation of dissimilar impressions on the hole bottom by teeth 106and teeth 116. Since outermost rows 104 and 114 of cones 102 and 112follow each other in substantially the same path around the well bottomas the rock bit rotates, tracking by the consecutive engagement of teeth106 and 116 with the formation is prevented.

In accordance with another preferred embodiment of the present inventionof FIG. 1D, a roller cone rock bit has a cone 132. Cone 132 has an innerrow 134, in which are located teeth 126. Teeth 126 are oriented at anangle A degrees to the center axis of cone 132. Also located in innerrow 134 are teeth 138. Teeth 138 are oriented at a an angle B degrees tothe center axis of cone 132. Since angle A and angle B are not equal inthis configuration, teeth 136 and teeth 138 are aligned at differentorientations. The difference in orientation causes the generation ofdissimilar impressions on the hole bottom by teeth 136 and teeth 138.Since inner row 134 of cone 132 drills a concentric ring in the holebottom without substantial overlap by the teeth of other cones, trackingby the consecutive engagement of teeth 136 and teeth 138 with theformation is prevented.

DEFINITIONS

Following are short definitions of the usual meanings of some of thetechnical terms which are used in the present application. (However,those of ordinary skill will recognize whether the context requires adifferent meaning.) Additional definitions can be found in the standardtechnical dictionaries and journals.

The “cones” in a roller cone bit need not be perfectly conical (norperfectly frustroconical), but often have a slightly swollen axialprofile.

-   Offset angle: the angular difference by which the axes of the cones    do not intersect the centerline of the borehole.-   Journal angle: the angle by which the centerline of the bearings    intersects the horizontal plane of the bottom of the hole.-   Gage row or heel row: the outermost row of teeth on a roller cone,    i.e. the teeth which come nearest to the outermost diameter of the    hole bottom.

According to a disclosed class of innovative embodiments, there isprovided: A roller cone bit comprising: a plurality ofnon-axially-symmetric teeth mounted on rotatable elements, wherein onesof said teeth which follow the same path on a cutting face havedifferent axial orientations; whereby the likelihood of tracking isreduced.

According to another disclosed class of innovative embodiments, there isprovided: A bit for downhole rotary drilling, comprising: a rotatableelement which includes a row of teeth; wherein a first one of said teethhas a first orientation and a second one of said teeth has a secondorientation which differs from said first orientation.

According to another disclosed class of innovative embodiments, there isprovided: A bit for downhole rotary drilling, comprising: a body havingan attachment portion capable of being attached to a drill string;cutting elements rotatably attached to said body, each said elementincluding multiple rows of teeth; wherein at least one of said rows onat least one said cutting element includes first and second teeth whichare non-axisymmetric; wherein said first tooth has a first orientationand said second tooth has a second orientation which differs from saidfirst orientation.

According to another disclosed class of innovative embodiments, there isprovided: A drill bit, comprising: a plurality of rotatable elementsmounted to roll along a cutting face when said drill bit is rotatedunder load, each said rotatable element having a heel row and inner rowsof teeth thereon; wherein ones of said teeth in the heel row of a firstone of said plurality of rotatable elements have crest orientationswhich are different from ones of said teeth in the heel row of a secondone of said plurality of rotatable elements.

According to another disclosed class of innovative embodiments, there isprovided: A roller cone bit comprising: a plurality of cones, each conehaving a circumferential outermost row containing a plurality of teeth;a first cone, having in its outermost row a first plurality of teethhaving a first axial orientation; and, a second cone, having in itsoutermost row, a second plurality of teeth having a second axialorientation which is not the same as said first axial orientation.

According to another disclosed class of innovative embodiments, there isprovided: A rotary drilling system, comprising: a drill string which isconnected to a bit; and a rotary drive which rotates at least part ofsaid drill string together with said bit; wherein said bit comprises aplurality of rotatable elements mounted to roll along a cutting facewhen said drill bit is rotated under load, each said rotatable elementhaving teeth thereon; wherein ones of said teeth which follow the samepath on a cutting face have different axial orientations.

According to another disclosed class of innovative embodiments, there isprovided: A rotary drilling system, comprising: a drill string which isconnected to a bit; and a rotary drive which rotates at least part ofsaid drill string together with said bit; wherein said bit comprises aplurality of rotatable elements mounted to roll along a cutting facewhen said drill bit is rotated under load, each said rotatable elementhaving an outer row and inner rows of teeth thereon; wherein a firstplurality of said teeth have crest orientations which are different fromthe crest orientations of a second plurality of teeth in said bit.

According to another disclosed class of innovative embodiments, there isprovided: A method of designing a bit for rotary drilling, comprisingthe actions of: determining an optimal range of orientations for teethfor each row of each cone; providing a variation in the orientations ofones of said teeth which follow the same path on a cutting face; wherebytracking is reduced.

According to another disclosed class of innovative embodiments, there isprovided: A method for rotary drilling, comprising the actions of: (a.)installing, on the drill string, a rotary drill bit whose toothorientation has been optimized to provide a variation in theorientations of ones of said teeth which follow the same path on acutting face; (b.) rotating at least a portion of said drill stringwhich includes said drill bit; whereby tracking is reduced.

MODIFICATIONS AND VARIATIONS

As will be recognized by those skilled in the art, the innovativeconcepts described in the present application can be modified and variedover a tremendous range of applications, and accordingly the scope ofpatented subject matter is not limited by any of the specific exemplaryteachings given.

Additional general background, which helps to show the knowledge ofthose skilled in the art regarding implementations and thepredictability of variations, may be found in the followingpublications, all of which are hereby incorporated by reference: APPLIEDDRILLING ENGINEERING, Adam T. Bourgoyne Jr. et al., Society of PetroleumEngineers Textbook series (1991), OIL AND GAS FIELD DEVELOPMENTTECHNIQUES: DRILLING, J.-P. Nguyen (translation 1996, from Frenchoriginal 1993), MAKING HOLE (1983) and DRILLING MUD (1984), both part ofthe Rotary Drilling Series, edited by Charles Kirkley.

None of the description in the present application should be read asimplying that any particular element, step, or function is an essentialelement which must be included in the claim scope: THE SCOPE OF PATENTEDSUBJECT MATTER IS DEFINED ONLY BY THE ALLOWED CLAIMS. Moreover, none ofthese claims are intended to invoke paragraph six of 35 USC section 112unless the exact words “means for” are followed by a participle.

1-19. (canceled)
 20. A roller cone drill bit, comprising: a plurality ofroller cones rotatably mounted on a bit body; and a plurality ofnon-axisymmetric cutting elements disposed in at least one row on eachof the roller cones, wherein on the at least one row of at least one ofthe plurality of roller cones at least one of the cutting elements isoriented at a different angle than the other ones of the cuttingelements on the at least one row.
 21. The roller cone drill bit asdefined in claim 20 further comprising, on each of the roller cones, atleast one cutting element being oriented at an angle different than theother ones of the cutting elements on the at least one row of thecutting elements.
 22. The roller cone drill bit as defined in claim 21further comprising at least one cutting element in each row on each ofthe roller cones being oriented at an angle different than the otherones of the cutting elements on each same row on each of the rollercones.
 23. The roller cone drill bit as defined in claim 20 wherein, oneach one of the rows on at least one cone, at least one cutting elementin each one of the rows is oriented at an angle different than the otherones of the cutting elements in a same one of the rows.
 24. The rollercone drill bit as defined in claim 20 wherein each of the other ones ofthe cutting elements is oriented so that its long dimension issubstantially parallel to an axis of the one of the roller cones onwhich it is disposed.
 25. The roller cone drill bit as defined in claim20 wherein each of the other ones of the cutting elements is oriented sothat its long dimension is substantially not parallel to an axis of theone of the roller cones on which it is disposed.
 26. A roller cone drillbit, comprising: a plurality of roller cones, each rotatably mounted ona bit body; a plurality of cutting elements on each of the cones, atleast one of the cutting elements being non-axisymmetric; and wherein anangle subtended between a long dimension of a crest of the at least onenon-axisymmetric cutting element and an axis of rotation of the cone onwhich the at least one cutting element is disposed, and a profile of theat least one non-axisymmetric cutting element are both selected tooptimize a value of the at least one drilling performance parameter. 27.The roller cone drill bit as defined in claim 26 wherein the longdimension of the crest of the at least one non-axisymmetric cuttingelement is oriented substantially not parallel to an axis of the one ofthe roller cones on which it is disposed.